This invention relates to a propelling mechanism and to a traveling device propelled thereby to travel through tortuous tubular passageways such as piping. More particularly the invention relates to a propelling mechanism which has traction wheels for driving, and which is capable of thus traveling in a freely steerable manner through a passageway having bends and constrictions as the pressure of the wheels on the inner surface of the passageway is automatically adjusted.
In recent years, moving inspection probes of miniature size for traveling through and inspecting the interiors of piping in installations such as nuclear power plants and chemical plants have been developed and reduced to practical use. In piping of the above mentioned kind, complicated piping layouts are often used with numerous Tee joints, elbows, and the like.
Furthermore, many constrictions in the pipe cross section due to deposits of accumulated matter and variations of the pipe diameter at fixtures such as reducers are encountered. For this reason, there has been a great need for a traveling device such as an inspection probe which can flex freely while traveling and at the same time can cope with variations of the inner diameter of the piping.
Furthermore an additional requirement is that the one or more propelling mechanisms provided in one traveling device have ample towing power for towing control and power supply cables and the like connected to the traveling device. Still another requirement is that the traveling device have a wheel-pressing mechanism for pressing traction wheels against the inner wall surface of the piping so that the traveling device can clamber safely up a vertical pipe.
With the aim of meeting these requirements, traveling devices in which resilient force-absorbing means such as springs are interposed between traction wheels and driving mechanisms have and are being proposed. In these traveling devices, the springs deflect and absorb variations in pipe diameter. Furthermore, a traveling device in which traction wheels are pressed against the inner wall surface of the pipe to increase the friction between the wheels and the pipe inner surface and thereby to obtain a large towing (traction) force, and which thereby can clamber up vertical pipes has also been proposed.
In the above described known traveling devices, however; it is necessary to provide each wheel with a driving device. For this reason, miniaturization of the entire device is difficult. Furthermore, the above mentioned pressing force on the wheels is determined by the degree of compression of the springs. Therefore, as the weight of the device increases, the inertial load of the springs increases, and the periodic damping decreases. For this reason, it is difficult to sustain constantly the pressing force of the wheels acting on the inner wall surface of the piping. Consequently stable traveling cannot be carried out.
Furthermore, since the above mentioned pressing force is determined by the degree of compression of the springs, the pressing force becomes large at places where the pipe inner diameter is small and, conversely, becomes small at places where the inner diameter is large. In actual practice, however, there is a necessity for means for adjusting the pressing force in accordance with the load. Such means must impart a large pressing force in cases such as that where the traveling device climbs a vertical pipe and that where another piece of equipment is towed through the piping.
Still another problem existing in the prior art is the complexity of construction of steering mechanisms for enabling the traveling devices to travel smoothly through bends and branch parts of the piping.